Crack Coalescence in Molded Gypsum and Carrara Marble: Part 1. Macroscopic Observations and Interpretation
- 1.8k Downloads
Cracking and coalescence behavior has been studied experimentally with prismatic laboratory-molded gypsum and Carrara marble specimens containing two parallel pre-existing open flaws. This was done at both the macroscopic and the microscopic scales, and the results are presented in two separate papers. This paper (the first of two) summarizes the macroscopic experimental results and investigates the influence of the different flaw geometries and material, on the cracking processes. In the companion paper (also in this issue), most of the macroscopic deformation and cracking processes shown in this present paper will be related to the underlying microscopic changes. In the present study, a high speed video system was used, which allowed us to precisely observe the cracking mechanisms. Nine crack coalescence categories with different crack types and trajectories were identified. The flaw inclination angle (β), the ligament length (L), that is, intact rock length between the flaws, and the bridging angle (α), that is, the inclination of a line linking up the inner flaw tips, between two flaws, had different effects on the coalescence patterns. One of the pronounced differences observed between marble and gypsum during the compression loading test was the development of macroscopic white patches prior to the initiation of macroscopic cracks in marble, but not in gypsum. Comparing the cracking and coalescence behaviors in the two tested materials, tensile cracking generally occurred more often in marble than in gypsum for the same flaw pair geometries.
KeywordsUniaxial compressive loading test High speed camera Tensile cracks Shear cracks Crack type classification scheme
The project is sponsored by the NSF Geomechanics and Geotechnical Systems Program under grant CMMI-0555053 and the US Department of Energy Geothermal Program under grant DE-FG36-06GO16061. The first author is also thankful to the support by the Croucher Foundation Scholarship (Hong Kong) and the Sir Edward Youde Memorial Fellowship (Hong Kong).
- Backers T, Dresen G, Rybacki E, Stephansson O (2004) New data on mode II fracture toughness of rock from the punchthrough shear test. Int J Rock Mech Min Sci 41(3):1–6Google Scholar
- Bobet A (1997) Fracture coalescence in rock materials: experimental observations and numerical predictions. ScD thesis, Massachusetts Institute of Technology, CambridgeGoogle Scholar
- Einstein HH, Hirschfeld RC (1973) Model studies on mechanics of jointed rocks. ASCE J Geotech Div 99:SM3Google Scholar
- Einstein HH, Nelson RA, Bruhn RW, Hirschfeld RC (1969) Model studies of jointed rock behavior. In: Proceedings of 11th symposium on rock mechanics, pp 83–103Google Scholar
- Ko TY, Einstein HH, Kemeny J (2006) Crack coalescence in brittle material under cyclic loading. Golden rocks 2006, Proceedings of the 41st US symposium on rock mechanics (USRMS): “50 years of rock mechanics—landmarks and future challenges”, Golden, Colorado, June 17–21, ARMA/USRMS 06-930Google Scholar
- Reyes O, Einstein HH (1991) Failure mechanism of fractured rock—a fracture coalescence model. In: Proceedings of the 7th international congress of rock mechanics, vol 1, Aachen, Germany, pp 333–340Google Scholar
- Wong NY (2008) Crack coalescence in molded gypsum and Carrara Marble, Ph.D. Thesis, Massachusetts Institute of Technology, Cambridge, MA, p 876Google Scholar
- Wong LNY, Einstein HH (2006) Fracturing behavior of prismatic specimens containing single flaws. In: Proceedings of the 41st US symposium on rock mechanics (USRMS): “50 years of rock mechanics—landmarks and future challenges”, Golden, Colorado, ARMA/USRMS 06-899Google Scholar
- Wong LNY, Einstein HH (2007) Coalescence behavior in Carrara marble and molded gypsum containing artificial flaw pairs under uniaxial compression. In: Proceedings of the 1st Canada-US rock mechanics symposium, Vancouver, Canada, pp 581–589Google Scholar
- Wong LNY, Einstein HH Systematic evaluation of cracking behavior in specimens containing single flaws under unaxial compression. Int J Rock Mech Min Sci (accepted)Google Scholar
- Wong LNY, Einstein HH Crack coalescence in molded gypsum and Carrara marble: part 2—microscopic observations and interpretation. Rock Mech Rock Eng (this issue)Google Scholar